1. Field of the Invention
This invention relates to a method of computer aided interpretation of retinal nerve fiber layer images, and more particularly to a method of mathematically analyzing such images after the images have been expressed in digital form.
2. Information Disclosure Statement
Over the immediate past few decades, some further understanding of glaucoma and related diseases has been gained. Ophthalmic medicine broadly equates retinal nerve fiber layer (RNFL) deterioration and degeneration to optic neuropathological conditions, especially glaucoma, and uses as diagnostic tools visual examination, intraocular pressure (IOP) measurements, eye fundus photography, manual and computerized visual field results, and ocular angiogram analysis. While not all of these tests are indicated for every patient, advances in technology have enhanced each of the previously named areas. As the disclosure which follows concerns ophthalmography and more specifically, eye fundus photography, the balance of this discussion is limited thereto. The Applicant is familiar with eye fundus camera literature in Class 351, Subclasses 006.000, 007.000, 013,000, 014.000, and 016.000 and is unaware of any applicable references contained therein. A pre-examination medical literature search was conducted and uncovered the following:
Caprioli; Joseph; et al. "Videographic Measurements of Optic Nerve Topography in Glaucoma," Investigative Opthalmology & Visual Science, Vol. 29, No. 8 (August, 1988) pp. 1294-1298.
Cooper, Richard L.; et al. "Computerized Densitometry of Red-Free Retinal Photographs Correlated with Automatic Perimetry," Current Eye Research, Vol. 7, No. 8 (1988) pp. 789-799.
Lundstrom, Mats, et al. "Computer Densitometry of Retinal Nerve Fibre Atrophy," Acta Ophthamologica, Vol. 58 (1980), pp. 639-644.
Mitra, Sunanda; et al. "Automated method for Fundus Image Registration and Analysis," Applied Optics, Vol. 27, No. 6 (Mar. 15, 1988), pp. 1107-1112.
Peli, Eli; et al. "Computerized Enhancement of Retinal Nerve Fiber Layer," Acta Ophthamologica, Vol. 64 (1986), pp. 113-122.
Caprioli et al. have used computerized digital analysis techniques of the optic nerve head to provide quantitative measurements of the optic nerve head topography. Cooper et al. have correlated retinal photographic density with field loss using histogram equalization. Mitra et al. have used spectrum analysis and cepstrum analysis to correct for rotational and translational shifts in image registration. Lundstrom et al have used computerized densitometry measurements to assess local density variation. Peli et al. have used digital analysis techniques, including contrast enhancement (histograph modification and extremum sharpening) for wedge defects; directional enhancement for slit defects; and, homomorphic filtering and adaptive enhancement for diffuse defects.
In the medical literature, there has been a widespread indication that early changes in retinal nerve fiber layer structure occur before measurable abnormalities are detected. While glaucoma is not fully understood, the structure of the RNFL has been studied extensively and it is known that, upon deterioration and degeneration of the RNFL, concomitant changes in optic nerve topography occur. Present ophthalmoscopic and ophthalmographic techniques do not yield sufficient topographic data.